Process for producing lead from lead sulfide containing materials



United States Patent PROCESS FOR PRODUCING LEAD FROM LEAD SULFIDECONTAINING MATERIALS vor der Hohe, Werner Carl-August Maelzer,

No Drawing. Application September 10, 1954, Serial No. 455,353

Claims priority, application Germany September It), 1953 13 Claims. (Cl.75--77) The present invention relates to an improved process forproducing lead from materials containing lead sulfide such as ores,concentrates, intermediate products or waste products containing leadsulfide, and is particularly adapted to the production of lead from suchmaterials having a high content of lead sulfide, for example, fromconcentrates containing 65 to 85% of lead.

Modern flotation processes yield lead ore concentrates which hardlycontain any gangue and in which the lead content has been concentratedto 65 to 85%. For example, concentrates are obtained containing 80%lead, 14% sulfur and 6% gangue. The smelting of such concentrates in thegenerally used shaft furnace processes requires a preliminary sinteringwith the addition of the supplements required for the shaft furnace. Inthe shaft furnace the lead concentrate is then reduced by the additionof coke and the agglomerate is reduced to raw lead and slag. Thereduction in the shaft furnace only pro eeeds without disturbances ifthe lead content of the charge is at most 50%, as, with higher leadcontents, the charge bakes together and becomes impermeable to gasbefore it has completely reacted. It is consequently customary to admixslag, lime and/ or silica with the concentrate either before or afterthe roasting before the charge is introduced into the shaft furnace inorder that it be diluted to a lead content of 50%. It is just suchdiluents which are separated in the flotation or in the shaft furnace,so that the advantages obtained by the concentration during flotation,except for savings in transportation, are substantially reduced as thethroughput through the shaft furnace is lowered proportionately to thedilution and the heat required per ton of lead produced iscorrespondingly increased.

One process for smelting of concentrates Without dilution has beenproposed, namely, the roasting-reaction process on Newman hearths orSchlippenbach plants. With such a process, about 60% of'the leadcontained in the ore is converted to raw lead on a hearth furnace. Thegray slag obtained in the hearth furnace is sintered and then smelted-ina shaft furnace with the addition of coke with a conversion of a further30% of the lead content of the ore into raw lead. A considerablequantity of dust occurs both in the hearth furnace as well as in theshaft furnace. Such dust approximately contains about of the leadoriginally contained in the ore and must be recovered by electrostaticgas cleaning apparatus. The high incidence of intermediate products richin lead renders it necessary to split up the manufacturing process intoseveral streams which entails an increase in labor costs. Also, as theflow of material is divided into several streams, the apparatuses do notoperate uniformly and it is difiicult to avoid danger to the operatorsfrom the large quantities of lead containing dust which occurs.Furthermore, the process entails the use of coke for the smelting of thegray lead containing slag in the shaft furnace.

bound sulfur is about 2:1.

, 2,797,158 Patented June 25 1957 The object of the present invention isa process for the efiicient recovery of lead from materials rich in leadwithout the necessity of using coke and without having to add anysubstantial quantities of foreign materials, particularly reducingmaterial such as coke, and in which the lead is produced at only onepoint and in which the product of dust is minimized.

In accordance with the invention it has been found that lead could beobtained from fine grained sulfidic lead ores or concentrates bygranulating such ores or concentrates, if desired, with the additionofoxidic lead ore, and partially roasting and sintering to produce amixture of lead sulfide and oxide and possibly lead sulfate whichcontains a sufiicient quantity of chemically bound oxygen that it can beconverted to lead and sulfur dioxide in a suitable furnace withoutfurther'addition of oxygen by the so-called roasting-reaction process.

In the roasting-reaction process, the chemically bound oxygen introducedinto the charge during roasting reacts with the chemically bound sulfurretained in the charge to produce metallic lead and sulfur dioxide. Theprimary reactions involved are represented by the following equations:

In accordance with the present invention it was found that the roastingof the fine grained ore or concentrate to produce a satisfactorilycoherent and gas permeable sinter with the desired ratio of chemicallybound oxygen to chemically bound sulfur is possible without thenecessity of previous granulation of the charge if recycled internalmaterial and/or fly ash is admixed with the fine I grained charge to besintered. The best results are obtained when the ratio of recycledmaterial and/or fly ash to ore or concentrate is more than 1:1 andpreferably 1.5 to 2:1. The term fly ash, as employed herein, is intendedto mean such fly :ash as occurs in the metallurgy of lead.

The sintering roasting can be effected in a known manner on amoving'sintering grate. If desired, a small quantity of finely dividedlime in the form of limestone, hydrated or unslaked lime can be admixedwith the charge to be sintered. The sulfide-sulfur content of the chargeto be sintered is adjusted in order to beable to operate with theoptimum sintering temperature. With most high percentage lead ores orconcentrates a 5-9, preferably about 7%, is suitable. The sintering iseffected with oxygen containing gases, such as, air or air in admixturewith recycled gas, care being taken that suflicient free oxygen ispresent therein to produce a sinter in which the molar ratio of boundoxygen to After the sintered product is discharged from the sinteringapparatus, the sinter is crushed and sieved. The quantity of sinteredproduct in the desired grain size required for the sinter roastingisrecycled and admixed with the subsequent ore or concentrate to beroasted :and sintered. The remaining sintered product is then chargedinto a furnace and rapidly heated to reaction temperature to producemetallic lead I tered product to reaction temperatures is etfected in asshort a time as possible.

The increase in speed of reaction attained by such high temperaturesreduces evaporation losses to a minimum. At the temperatures nor-'mally, employed for such internal reaction for the production of lead,which are under about 1000 C. and usu- 3 ally lie between 800 and 1000"C., considerably greater evaporation. losses occur.

If the nature of the ore, and especially the composition of its gangue,requies it, it can, in exceptional cases, beneeessary to add smallquantities of additional materials such as sand, soda, limestone or ironcontaining materials (pyrites, roasted pyrites, iron ores) in order toassure the production of a good and sufficiently liquid slag. As thegangue content of a good lead ore concentrate does not exceed about 58%,the quantity of additional materials which may be required, if at all,is very small and usually only 2-5% of the quantity of the concentrate.

It has been found that the rapid heating to the high temperatuers isexceptionally advantageously carried out in a rotary drum flame furnacerotating about a horizontal axis, especially one whose length is nogreater than about twice its diameter, and preferably one whose lengthis about equal to that of its diameter. As the flame path reverses inthe furnace, the heat introduced thereby into the furnace is rapidly anddirectly transferred to the furnace charge during rotation of thefurnace and substantially lower evaporation losses occur than when theusual flameand rotary furnaces are employed.

It was also found according to the invention that it is expedient not tocarry out the preliminary roasting and sintering so that the exact ratioof lead bound sulfur and lead bound oxygen required for the subsequentinner conversion is achieved thereby, as the exact control of such ratiois difficult to achieve upon a commercial scale operation. The roastingand sintering is, however, carried out so that the molar ratio of leadbound oxygen to lead bound sulfur in the resulting sinter isapproximately 2:1 but that such sinter contains either an excess ordeficiency in oxygen. By making slight changes in the roasting andsintering conditions, sintered products containing an excess of oxygenand sintered products containing a deficiency in oxygen are alternatelyproduced and by mixing such sintered products the optimum 0:8 ratio isproduced before the charge is introduced into the rotary flame furnace.The oxygen content in the sintered product can be varied by adjustingthe velocity of the grate, the quantity of recycled material admixedwith the charge, the thickness of the charge as well as the pressuredifferential above and below the charge. It is furthermore also possibleto smelt with an oxidizing flame. and compensate for the oxidizingdegree of the flame by a corresponding oxygen deficiency in the solidsinter charged into the smelting furnace. In practice it was found thatthe optimum 0:8 ratio in the charge when employing an oxidizing flameduring the smelting is 1.90 to 1.95 mol 0:1 mol S. The simplestprocedure is to adjust the 0:8 ratio, only approximately, by mixing thedifferent sintered products and to adjust such ratio to the desiredvalue during the smelting operation with reference to the oxidizingdegree of the flame employed by small appropriate additions of sinterwith excess or deficiency in oxygen content or, if desired, with deadroasted or unroasted sulfidic material. This mode of operation isadvantageous in that it is simpler to adjust the composition of thecharge with reference to the oxidizing degree of the flame employed bysuitable additions of solid materials to the charge than to adjust theoxidizing .degree of the flame to conform to that required for thecharge. The procedure according to the invention furthermore renders itpractical to employ an oxidizing flame for the smelting operation sothat the highest temperature attainable with the fuel employed can beattained so that rapid heating of the charge with correspondingly lowerevaporation losses is promoted. V

Inthetreatment of some ores asmall quantity of a slag like leadcontaining residue can, remain. after completition of the smeltingreaction. The residue preferably.

is retained in the smelting furnace and retreated with the next charge.After several charges the. lead content 4v thereof is decreased to suchan extent that it can be discarded.

The following example will serve to illustrate the process according tothe invention:

Example 16.6 parts by weight of a sulfidic lead ore of the composition IPercent Pb 80.2 S 14.36 Zn 3.2 CaO 0.5

was mixed with 3.4 parts by weight of an oxidic ore of the followingcomposition and 2.0 parts by weight of a mixture of fly ashes of varyingorigin primarily fromthe sintering apparatus and the rotary flamesmelting furnace. The fly ash mixture contained 71.3% Pb and 8.0% S.This mixture was admixed with 20 parts. by weight of recycled sinteredmaterial of a grain size of 4l2 mm. with the addition of 6-7% of H20based upon the whole admixture. The recycled sintered material contained81.0% Pb of which 40.6% was metallic Pb, 16.4% was in the form of PbS(18.9% PbS), 13.6% was in the form of PbO (14.7% PbO) and 10.4% was inthe form of PbSO4 (15.2% PbSOt).

The resulting admixture was sintered in the following manner on asintering apparatus:

A grate covering of finished sintered product from a previous charge ofthe same composition of the recycled sintered material in the chargeabout 20 mm. thick was first applied to the moving grate of thesintering apparatus. The grain size of such grate covering was 12-20 mm.An ignition layer 30 mm. thick of the some composition as the charge tobe sintered except that the fly ash was omitted was applied over thegrate covering. This ignition layer was ignited under the ignition hoodof the sintering apparatus while air was drawn downwardly therethrough.Thereafter a mm. layer of the admixture to be sintered was applied overthe ignited ignition layer and the entire charge on the grate wassintered while air was passed upwardly through the charge.

The finished sintered product was of the same composition as thatindicated above for the recycled sintered material admixed with thecharge to be sintered. The weight ratio of oxygen bound to lead tosulfur bound to lead in the sintered product was 1.05:1 whichcorresponds to a molar ratio of 2.1:1.

One part of this sintered product was admixed with 1.2 parts of asintered product produced in a similar manner having a deficiency inlead bound oxygen containing 80.5% Pb of which 37.4% was in the form ofmetallic lead, 9.3% was in the form of PbSO4 (13.6% PbSOr), 19.9% was inthe form of P138 (23.0% PbS) and 16.6% Was in the form of PbO (17.9%PbO). The molar ratio of lead bound oxygen to lead bound sulfur thereintherefore was 1.81:1. The resulting mixed sintered product therefore hada molar ratio of lead bound oxygen to lead bound sulfur of 1.93:1. Theslight deficiency in oxygen in the mixed sintered product was found inpractice to be the optimum for counteracting the oxidizing action oftheflame in the rotary smelting furnace.

kilograms of this mixed sintered product were introducedinto a rotaryflame furnace having an internal diameter of 0.7 meter-and'an internallength of 0.7 meter which had been preheated to 1200 C. The period re,-

quired for the charging of the furnace was minutes. The temperature ofthe furnace which had been reduced by the introduction of the coldcharge and the ensuing reaction was again raised to the original 1200 C.in 140 minutes and then maintained at such temperature for a further 10minutes. The furnace was then tapped. 110 kg. of raw lead, 4.5 kg. offly ash containing 70.5% Pb and 29.0 kg. of slag containing 28.8% Pbwere produced. The yield obtained upon the basis of the 150 kg. chargeis not entirely correct as it is impossible to prevent slag from aprevious charge to be admixed with the slag of the new charge or toprevent a certain quantity of the slag from being retained in thefurnace.

We claim:

1. A process for the production of metallic lead from materialscontaining lead sulfide with a content of at least 50% Pb whichcomprises sintering said lead sulfide containing material withoutaddition of fuel in admixture with at least one material selected fromthe group consisting of fly ash and recycled sintered material underoxidizing roasting conditions to provide about a sufficient quantity ofoxygen bound to lead in the sintered product to react upon heating withthe sulfur bound to lead retained in the sintered product, and heating acharge of the sintered product without addition of fuel to reactiontemperatures to produce metallic lead and volatile sulfur compounds.

2. A process in accordance with claim 1 in which the admixture of thelead sulfide containing material is alternately sintered underconditions producing an excess of lead bound oxygen in the sinteredproduct and under conditions producing a deficiency of lead bound oxygenin the sintered product, and mixing the sintered products obtained toproduce a sintered product containing an optimum lead bound oxygen tolead bound sulfur before such sintered product is heated to reactiontemperatures to produce the metallic lead and volatile sulfur compounds.

3. A process in accordance with claim 1 in which the molar ratio of leadbound oxygen to lead bound sulfur is 1.90 to 1.95 :1 in the sinteredproduct heated to reaction temperatures and the heating to reactiontemperatures is efiected With an oxidizing flame.

4. A process in accordance with claim 1 comprising in addition addingsmall quantities of a material selected from the group consisting oflead bound oxygen and lead bound sulfur containing material while thesintered product is heated to reaction temperatures to adjust the leadbound oxygen to lead bound sulfur in the charge.

5. A process in accordance with claim 1 in which the ratio of thematerial selected from the group consisting of recycled sinteredmaterial and fly ash to the lead sulfide containing material is greaterthan 1:1.

6. A process in accordance with claim 1 in which the ratio of thematerial selected from the group consisting of recycled sinteredmaterial and fly ash to the lead sulfide containing material is 1.5 to2:1.

7. A process in accordance with claim 1 comprising in addition admixinga small quantity of lime with the admixture to be sintered.

8. A process for the production of metallic lead from materialscontaining lead sulfide with a content of at least Pb which comprisessintering said lead sulfide containing material without addition of fuelin admixture with at least one material selected from the groupconsisting of fly ash and recycled sintered material under oxidizingroasting conditions to provide about a sufiicient quantity of oxygenbound to lead in the sintered product to react upon heating with thesulfur bound to lead retained in the sintered product, and rapidlyheating a charge of the sintered product Without addition of fuel toreaction temperatures over 1100" C. to produce metallic lead andvolatile sulfur compounds.

9. A process in accordance with claim 8 in which said reactiontemperatures are between 1200 C. and 1250 C 10. A process in accordancewith claim 8 in which said heating to reaction temperatures is effectedin rotary flame furnaces rotating about a horizontal axis.

11. A process in accordance with claim 10 in which the ratio of thediameter to the length of said flame furnace is at most 1:2.

12. A process in accordance with claim 10 in which the ratio of thediameter to the length of said flame furnace is about 1:1.

13. A process in accordance with claim 8 comprising in additionseparating the lead produced from any slag produced and heating suchslag in admixture with further quantities of said sintered product toreaction temperatures to produce lead and volatile sulfur compounds.

References Cited in the file of this patent UNITED STATES PATENTS2,416,628 Kalling Feb. 25, 1947 2,660,525 Foster Nov. 24, 1953 FOREIGNPATENTS 482,224 Great Britain Mar. 25, 1938

1.A PROCESS FOR THE PRODUCTION OF METALLIC LEAD FROM MATERIALSCONTAINING LEAD SULFIDE WITH A CONTENT OF AT LEAST 50% PB WHICHCOMPRISES SINTERING SAID LEAD SULFIDE CONTAINING MATERIAL WITHOUTADDITION OF FUEL IN ADMIXTURE WITH AT LEAST ONE MATERIAL SELECTED FROMTHE GROUP CONSISTING OF FLY ASH AND RECYCLED SINTERED MATERIAL UNDEROXIDIZING ROASTING CONDITIONS TO PROVIDE ABOUT A SUFFICIENT QUANTITY OFOXYGEN BOUND TO LEAD IN THE SINTERED PRODUCT TO REACT UPON HEATING WITHTHE SULFUR BOUND TO LEAD RETAINED IN THE SINTERED PRODUCT, AND HEATING ACHARGE OF THE SINTERED PRODUCT WITHOUT ADDITION OF FUEL TO REACTIONTEMPERATURES TO PRODUCE METALLIC LEAD AND VOLATILE SULFUR COMPOUNDS.